During the construction of a building there are many occasions where a plurality of pieces, such as sheets of sheet rock, have to be cut along a selected angle, for example along a line to match a roof-line which forms a selected angle, such as 30 degrees with the horizontal. Conventionally this is done by taking specific measurements at locations of the structure where the piece is to be attached corresponding to the two extremities of each piece, marking these points on the piece and drawing or striking a guide mark between the points and then cutting the piece along the mark. This process is repeated with each piece to be placed contiguous with the roof-line. Not only is this a time consuming task but the possibility of making errors increases with each separate step concomitantly with the possibility of wasting material due to such errors. Since labor comprises a large proportion of the total cost of construction, it would be very desirable to decrease time involved in tailoring various component parts of the building as well as to minimize loss of material due to errors in taking and transferring measurements to the construction materials to be cut.